The work of professor Adrian Raftery, at the University of Washington, and his international research team, including UN experts, published in September 2014, has overturned 20 years of consensus – that global population, and the stresses it brings, will peak and plateau by 2050 at about 9bn people. This study for the first time uses advanced statistics to place convincing upper and lower limits on future population growth. He and others (such as Simon Ross, chief executive of Population Matters a thinktank supported by naturalist Sir David Attenborough

David Attenborough

and scientist James Lovelock) stress that it should be included in the issues and goals on the UN-led sustainable development agenda.

Up till 2015 the estimate of the global fertility rate (number of children per woman) had declined to 2.42. But from then on there has a slowdown in the pace of fertility decline. There are higher fertility rates in Africa especially. In countries like Nigeria, the continent’s most populous nation, the decline has stalled completely with the average woman bearing six children. The cause of the stalled fertility rate is two-fold, said Raftery: a failure to meet the need for contraception and a continued preference for large families. “The unmet need for contraception – at 25% of women – has not changed in for 20 years,” he said. And “the preference for large families is linked to lack of female education which limits women’s life choices”. In Nigeria, 28% of girls still do not complete primary education.

An alternative scenario is given by the statistician Jorgen Randers (one of the co-authors of Limits to Growth), who argues that traditional projections insufficiently take into account the downward impact of global urbanization on fertility.

Jorgen Randers

Randers’ “most likely scenario” reveals a peak in the world population in the early 2040s at about 8.1 billion people, followed by decline. In China in 2015, for example, a baby boom is predicted (possibly 6M more births a year) after raising the family planning limit from one to two children per woman. This may balance the ageing population a bit, but it is expected to be short-lived as social and economic factors accompanying urbanisation will play a part: the cost of raising children and raising the quality of their lives is high in cities (childcare, education, rents, commuting, uncertainty in the job market).

How far and when all countries reach the stage where birth and death rates are in balance and the rate of population growth goes back to where it was in agrarian economies, 0.5% a year is uncertain, and unlikely in this century. Hopefully though fertility rates will come down to a global average nearer to 2 per woman in the population.

Another population concern is the rising life expectancy and ageing populations currently seen in Europe and Japan, which raises questions about how working populations will support large numbers of elderly people. But the new research shows the same issue will affect countries whose populations are very young today.